The reaction of inorganic materials in the past has called for admixture of the materials in the reaction vessel followed by the application of heat. Many times this calls for a special design or steps during the reaction process to achieve adequate reaction products. One such product is Portland cement.
The prior art has seen many different approaches to the manufacture of cement, ranging from the earliest recorded history to modern day methods of manufacturing Portland cement as illustrative of the cementitious products. The conventional processes in this country for manufacturing cementitious products have generally comprised admixing predetermined portions of calcareous and argillaceous, or siliceous, materials. The materials may be admixed with water to form a slurry or may be dried to form a dry, raw meal. In any event, the admixture is continuously fed into and burned within a cement forming kiln to form clinker. The resulting clinker is mixed and pulverized with gypsum to form dry powdered modern day Portland cement.
The calcareous material may consist of limestone, marble, chalk, oyster shells and the like. The argillaceous material may consist of clay, shale, slate, slag, fly ash, sand and the like. The proportions of these ingredients in the mixtures determine the resulting chemical composition of the clinker and the finished cement. Additives may be blended with one or more of the mixtures to provide the characteristics for each predetermined type of cement for the final cementing job to be done. The different types of Portland cement are well recognized and defined by the American Society of Testing Materials (ASTM). The most commonly manufactured cement is known as Type I, or general purpose cement. The remaining four types, Types II-V, are referred to as special purpose cements. These special purpose cements differ in the proportions of the respective ingredients and are usually manufactured in lesser quantities.
To try to provide the desirable features of manufacture; such as, those delineated hereinafter, a wide variety of artifices have been resorted to in the prior art. As noted in my U.S. Pat. No. 4,026,717, entitled "Economical, Finely Controlled Cement Production"; U.S. patents as early as 1883, illustrated by U.S. Pat. No. 274,288, have disclosed addition to fuel with argillo-calcareous raw materials for making cement. Many patents have issued since then with a similar idea of introducing calcareous material into the burning zone of a kiln and are typified by U.S. Pat. Nos. 1,728,828; 3,589,920. Patents such as U.S. Pat. No. 2,477,262 describe and claim the classic insufflation process. Patents such as U.S. Pat. Nos. 2,600,515 and 3,437,329 describe processes for operating a rotary cement kiln in which special additives are introduced into the burning zone of the kiln to provide the desired properties as they traverse upwardly through the kiln, meeting the downcoming admixture.
Other pertinent art includes U.S. Pat. No. 2,745,657 in which a solid, high ash fuel is burned in a special burner to produce a slag and then the burner is tapped off to withdraw the molten slag from the bottom.
Early patents such as U.S. Pat. No. 811,902 in 1906 show the use of tailings, of copper ore, for example, in a cement making process. U.S. Pat. No. 1,567,934 shows ore and cement making material smelted together to reduce the ore. U.S. Pat. No. 3,759,730 shows power station ash mixed with calcium carbonate and fired at 1300.degree. C. (Centigrade or Celsius), then at 1500.degree. C. and ground. U.S. Pat. No. 4,080,219 shows waste heat passed in heat exchange with wet materials for making cement.
One of the more pertinent modern patents is U.S. Pat. No. 4,174,974 showing coal ash slag used to produce cement; for example, with calcium oxide. The primary thrust is, however to increase the efficiency of a gasifier. U.S. Pat. No. 4,217,143 shows production of cement with calcium oxide, silica, and alumina ground to 200 mesh, dried to less 5% water, blended and compounded in a high velocity mill. U.S. Pat. No. 4,265,671 shows cement clinker fed into the top and bottom of a rotary kiln to produce cement. Despite the wide variety of approaches tried, the prior art has not achieved and provided a plurality of desirable features such as those delineated hereinafter.
1. The method and apparatus should enable using less expensive fuels of a quality less than that currently demanded.
2. Ideally the method and apparatus should eliminate noxious contaminants automatically from such relatively inexpensive fuels without requiring expensive scrubbing towers or the like for removing sulfur-containing pollution gases.
3. The apparatus and method should significantly reduce the cost, as by eliminating the crushing and grinding costs at the product end of the process.
4. The method and apparatus can be used to reduce disposal costs for disposing of fly ash and modify the fly ash through a phase chemistry modification such that it produces a hydraulic fly ash or other cementitious products.
5. The apparatus and method should be flexible enough to enable manufacturing cements of different compositions readily without necessitating long periods of time to change over the operation of a kiln and related accessories and without requiring special purpose kilns.
6. Ideally the method and apparatus should provide the flexibility of operating this process in conjunction with another process, such as generation of electricity, and provide more than 100% trade off with value of any power lost as compared with the value of products produced.
7. The apparatus and method should provide the flexibility of being able to intergrind clinker or the like from one boiler with fly ash or the like from another to provide any desired final cementitious product.
8. Finally, the method and apparatus should allay the tremendous problem of exceptionally large capital outlays for new kilns and accessories, such as employed in current modern day cement making plants.
As can be seen from the discussion of the prior art, none of the prior art provides the delineated advantages.